[xml] Make __xmlDoValidityCheckingDefaultValue and __xmlLoadExtDtdDefaultValue public

[ÐÐÐÑÑ ÐÐÑÐÐ <pashev igor gmail com>]

/* Please CC me */

Currently functionsÂ__xmlDoValidityCheckingDefaultValue() andÂ__xmlLoadExtDtdDefaultValue() has no version symbol.

This can cause an issue:

Suppose libxml is linked with GNU ld and libxml consumer is linked with solaris ld.

Solaris ld always assing "base version" to unversioned symbols [1], this is equivalent

to GNU ld with optionsÂ--default-imported-symver andÂ--default-symver. Thus

if libpool is linked via solaris ld and libxml - via GNU ld, we have:

debian/tmp/usr/lib/x86_64-illumos//libpool.so: undefined reference to `__xmlDoValidityCheckingDefaultValue libxml2 so 2'

debian/tmp/usr/lib/x86_64-illumos//libpool.so: undefined reference to `__xmlLoadExtDtdDefaultValue libxml2 so 2'

[1]Âhttps://github.com/illumos/illumos-gate/blob/master/usr/src/cmd/sgs/libld/common/version.c#L948